OBJECTIVES Despite the lack of evidence-based information on their clinical and cost-effectiveness, surgery and primary endocrine therapy (PET) are the most commonly used initial treatment strategies for older women with primary breast cancer in the United Kingdom (UK). To evaluate the cost-effectiveness of PET and surgery, a decision analytical modelling is necessary. This systematic review aimed to summarise the modelling methodologies from the literature to inform the model design in older women.  METHODS An electronic database search was conducted using NHS Economic Evaluation Database, Cochrane Library, Ovid Medline, PubMed, and EMBASE to identify full economic evaluations that compared different treatment strategies in postmenopausal women with primary breast cancer. Quality and modelling methodologies of included studies were assessed and summarised.  RESULTS All the 31 included studies assessed surgery and none assessed PET as the initial treatment. Most included economic studies used a Markov model with life-time horizon and 1-year cycle length. Nine studies which included sub-group analysis for older women (over 65 years old) used similar economic models and transition states with younger women (50 to 65 years old). The key disease-related health states were disease-free, recurrence, and death. Recurrence was mostly separated into loco-regional and distant recurrence.  CONCLUSIONS This systematic review can inform the design of an economic model comparing PET with surgery as initial treatment in older women based on the following assumptions: (1) health states are applicable across age groups; (2) transition states for modelling surgery in the literature are transferable to model the same treatment for older women; (3) metastasis transition states including progression, progression-free, and death can be used to model the PET pathway. Future study will validate this model by using a longitudinal dataset of older women with primary breast cancer, and synthesize data from different data sources to populate this economic model.